This invention relates to corrosion resistant magnetic alloys, and in particular to such an alloy having a unique combination of corrosion resistance and magnetic properties and to the use of such an alloy in a magnetic component for a magnetically actuated device.
Magnetically actuated devices, such as solenoid valves and relays, have been used in industrial and scientific systems for controlling the operations of those systems. In particular, solenoid valves are used to control the flow of fluids in chemical processes. Such devices include a magnetic coil and a moving magnetic core or plunger. In a typical arrangement, the coil surrounds the plunger such that when the coil is energized with electric current, a magnetic field is induced in the interior of the coil. The plunger is formed of a soft magnetic steel. A spring holds the plunger in a first position such that the device is either normally open or closed. When the coil is energized, the induced magnetic field causes the plunger to move to a second position to either close the device, if it is normally open, or open it, if it is normally closed. It is desirable that the material used to make the plunger have good magnetic properties, principally, a low coercive force and a high saturation induction.
The plunger is often in direct contact with the local environment and, in the case of the solenoid valve, with the fluid that is being controlled. For that reason, it is desirable that the plunger be formed of a material that has good resistance to corrosion because many such environments and fluids are corrosive and will corrode the plunger, which may cause the device to malfunction or the valve to leak or become inoperative.
Corrosion resistant, magnetic alloys are known that are suitable for use in components for solenoid valves. The weight percent compositions of two of the known alloys are set forth below.
The balance of each of those alloys is iron and usual impurities.
Alloys A and B provide acceptable magnetic properties, particularly a high magnetic permeability, low coercive force, and low residual induction. These alloys also provide good corrosion resistance for many types of solenoid valves. Consequently, these alloys have been widely used in the solenoid valve market. However, a need has arisen for greater corrosion resistance than Alloys A and B are able to provide, coupled with magnetic properties that are at least as good as the magnetic properties of Alloys A and B. The demand for better corrosion resistance is also coupled with a need for a soft magnetic material that is metallurgically clean. This need has arisen particularly in the semiconductor industry where high purity requirements are prevalent.
Another known alloy, Alloy C, has the following nominal weight percent composition.
The balance of that alloy is iron and usual impurities. Alloy C is known for its controlled thermal expansion characteristic. Consequently, it has been used substantially exclusively for glass-to-metal seals in electronic vacuum tubes and in incandescent and fluorescent lamps.
In accordance with one aspect of the present invention, there is provided a corrosion resistant, soft magnetic, ferritic steel alloy having the following broad and preferred compositions in weight percent.
The balance of each composition is essentially iron and the usual impurities found in similar grades of ferritic stainless steels. Here and throughout this specification the term xe2x80x9cpercentxe2x80x9d or the symbol xe2x80x9c%xe2x80x9d means percent by weight unless otherwise indicated.
The foregoing tabulation is provided as a convenient summary and is not intended to restrict the lower and upper values of the ranges of the individual elements of the alloy of this invention for use in combination with each other, or to restrict the ranges of the elements for use solely in combination with each other. Thus, one or more of the element ranges of the broad composition can be used with one or more of the other ranges for the remaining elements in the preferred composition. In addition, a minimum or maximum for an element of the broad composition can be used with the maximum or minimum for that element from the preferred composition.
In accordance with another aspect of this invention, there is provided a magnetic component for a magnetically actuated device. The magnetic component is formed of a corrosion resistant magnetic alloy having the broad and preferred weight percent compositions identified above.
In accordance with a further aspect of this invention, there is provided a solenoid valve that includes a housing having first and second channels formed therein such that said first and second channels meet at an intersection. The first channel has an inlet and an outlet and is adapted for conducting a fluid, such as a gas or liquid. A magnetic coil disposed in the housing such that it substantially surrounds at least a portion of the second channel. A magnetic core is movably disposed in the second channel between the magnetic coil and the intersection of the first and second channels such that when it is displaced within the second channel, a portion of said magnetic core moves into the first channel to close the first channel. The magnetic coil is operatively connected to a source of electric current for energizing the coil.